import java.util.Scanner;

public class TUTU {
    public static void main(String[] args) {
        int qianyi = 1;
        int qianer = 1;
        int san=2;
        int dangyue = 0;
        int n;

        Scanner input = new Scanner(System.in);
        System.out.println("请输入月份");
        int yue=input.nextInt();
        for (int i=0;i<yue-2;i++){
        dangyue=qianyi+qianer;
        n=qianyi;
        qianyi=dangyue;
        qianer=n;
    }
        System.out.println(dangyue);
}
}